Additive layer manufacturing (ALM) methods are known. In these methods a component is built up layer by layer until the 3D component is defined. In some ALM methods, layers are created by selective treatment of layers within a mass of particulate material, the treatment causing cohesion of selected regions of particulates into a solid mass. For example, the particulate is a ferrous or non-ferrous alloy powder and the treatment involves local heating using a laser or electron beam. Specific examples of such ALM methods include (without limitation); laser sintering, laser melting and electron beam melting (EBM). Such methods are sometimes known as powder-bed ALM methods.
ALM techniques are known for use in defining complex geometries to high tolerances and can be used as an alternative to casting. However, such methods are not ideally suited to some conventionally used core geometries. For example, where the ALM process uses a bed of particulate material, it is necessary to remove all the untreated particulate from cavities in the defined component. This is more difficult than leeching and removing a more fluid core in a casting process. Adopting the same core geometries as in a casting method can result in un-treated particulate materials becoming stuck in the bottoms and corners of the core cavity. During subsequent heat treatments, these powders sinter in place altering the intended design of the component to the possible detriment of the performance of the component.
Cast components are often used in gas turbine engines to define complex aerodynamic shapes. The casting process and materials used provide materials with very specific mechanical properties which need to be preserved in an environment where they are exposed to extremes of temperature and pressure.
Hollow cavities are provided within these components and serve to minimise weight, reduce material costs and also provide a conduit through which coolant fluids can be delivered to cool the cast components ensuring that surfaces of the components do not exceed critical temperatures which would affect their mechanical integrity. It is known to include in these cavities arrays of pins or pedestals which increase surface areas of internal surfaces allowing more rapid heat exchange. Incomplete evacuation of core cavities in such designs can be detrimental to the performance of the end product and may lead to scrappage of parts at considerable expense to the manufacturer and so cannot be tolerated.
For optimum cooling efficiency, it is sometimes desirable to have pedestals across as wide an internal surface of the cavity as is available. In some known arrangements, pedestals coincide with cavity walls. Whilst beneficial for cooling, this presents a potential problem if a powder ALM method were to be used as an alternative method of manufacture of the component, since they present tight radii at the intersection with the wall which can lead to trapping of powder and the associated problems discussed above. Consequently, a component designed for powder ALM manufacture is typically simplified by removing or repositioning pedestals which would otherwise coincide with the cavity wall leaving a clear route adjacent the wall for the simple removal of excess powder.